A metallocene may be described as an LM, where L is a substituted or unsubstituted cyclopentadienyl, indenyl or fluorenyl moiety, and M is from the group of transition metals Group IVB, (e.g., titanium, zirconium, hafnium), Group VB (e.g., vanadium, niobium, tantalum), Group VIIIB (e.g., iron, cobalt, nickel, ruthenium), and the lanthanide series (e.g., lanthanum). In all metallocenes, the various metallic species interact with a cyclopentadienyl moiety, which is either part of a larger organic structure (e.g., indenyl or fluorenyl) or with a simple cyclopentadienyl moiety (e.g., C5H5).
Metallocenes are used as catalysts for the polymerization of olefins. The resulting polymers have controlled tacticity, narrow molecular weight distribution and well-characterized molecular structure. Other uses for metallocenes include the manufacture of acetic acid, a fuel additive for antiknock, an antitumor agent in the medical field, and a fire retardant.